The programme also worked on behalf of 15 other cooperative societies to negotiate equivalent purchasing deals for renewable energy.

In its 2010 Sustainability Report, released yesterday, it was revealed that efforts to increase the amount of self-generated electricity are under way. Last year 24,000 MWh (2.1 per cent of all power used) was provided by the group's own wind turbines in Coldham, Cambridgeshire.

Planning permission has now been granted to extend the Coldham plant and to build a 14-turbine farm in Yorkshire capable of producing 28,000 MWh. However, permission to build a third wind farm was refused in April. An appeal against the decision has been lodged.

Overall, The Co-operative Group is one of the largest purchasers of renewable energy in the world. Concerted efforts by the company to improve its sustainability have led it to be named as one of the top 60 'green' companies in the UK by The Sunday Times (third in 2011, fourth in 2010).

Last year it was revealed that by removing all plastic sheaves from the group's stock of cucumbers it was able to cut eight tonnes of plastic from the supply chain. The Institute of Grocery Distribution (IGD) praised the 'naked cucumber' initiative as an example of sustainability best practice.